The present invention relates to flow control devices and, particularly, to valves of the type generally known as "soft" seated check valves. More specifically, this invention is directed to enhancing the performance of check valves, especially at low back pressure and in corrosive environments, and to a method of fabricating a corrosion resistant check valve characterized by such enhanced performance.
Soft seated check valves are generally of two types, ball cone and tapered plug. Although conventional valves of these types can be effective in checking the reverse flow of fluid though a line, their performance under low back pressure has often been unsatisfactory. The ball in the ball type valve is porous, and the mounting and operating characteristics are somewhat complicated, so that such valves are not easy to repair while in line. The tapered plug valves are typically of simpler design and more readily accessible for repair, but these types, even when new, have difficulty providing a good seal at low back pressure.
An exemplary prior art tapered plug check valve is disclosed in U.S. Pat. No. 3,677,286, in which a valve chamber is located between an inlet channel and an outlet channel, and a valve seat is located between the inlet channel and the valve chamber. A valve plug or plunger is supported in registration with the valve seat for engagement thereof when the fluid pressure in the chamber exceeds the pressure in the inlet channel. The sealing effect is accomplished by the mating of two tapered surfaces in a wedge-like action. At low seating pressure, the wedge-type interaction between the valve seat is applied over a relatively large contact area and a full circumferential seal cannot be assured. At very high back seating pressure, the molded valve seat disclosed in the referenced patent is subject to being pushed through the passageway between the chamber and the inlet channel, thereby destroying the seal and resulting in valve failure.